The present invention relates to a surface acoustic wave transducer.
A surface acoustic wave transducer comprises a substrate made of piezoelectric material, a first comb-shaped electrode formed on one surface of the substrate, and a second comb-shaped electrode formed on the surface of the substrate. The first and second comb-shaped electrodes have each a plurality of strips. The strips of the first electrode are interdigitated with those of the second electrode.
When a high-frequency signal voltage is applied between the first and second electrodes, the substrate vibrates, thereby generating surface acoustic waves. As the waves propagate along the surface of the substrate, they are reflected from the edges of the strips of both electrodes. The reflected waves form spurious components generally called "acoustic reflection components". In the meantime, the waves propagating under the comb-shaped electrode connected to a prescribed external load will reinduce high-frequency signals on the comb-shaped electrode, thus producing spurious components generally called "electrical reflection components". Both types of reflection components will appear in the output signals of a filter or a delay line composed of the transducer, in the form of a triple transit echo. They deteriorate the characteristic of the filter or delay line.
This problem will be solved if the transducer is so designed as to make the acoustic reflection components cancel out the electrical reflection components over a broad range of frequencies. Several attempts have been made to provide such a surface acoustic wave transducer, but have failed.